Organopolysiloxanes of improved adhesion containing peroxides



Patented May 19, 1953 GRG'ANQPOLYSILOXANESOF IMPRGVED ADHESIONCONTAINING rERoxmEs' Robert. Smith-Johannsen and Giirtis' S;- 0live'iSchenectady, N. Y., assignnrs to General151cc-- tric Company, acorporation of New York:

No Drawing. Application November 21, 1950,

Serial No. 19639445 15 Claims.

This invention is concerned. with organopolysiloxanes particularlysilicone rubbers having im; proved adhesion to solid surfaces. Moreparticularly, the invention relates to a composition of mattercomprising (1) a titanium dioxidefilled organopolysiloxane convertible,e. g., by heat, to the solid; elastic state, (2) a cure accelerator for(1), and (3) less than 0.5%, by ht, based: on: the. weight oftheorganopolysiloxane, of an organic peroxide compound (so identifiedhereinafter in the specification and claims) selected from theclassconsisting of ditertiary butyl .diperphthalate, tertiary butylhydroperoxide, dipersuccinic acid, ditertiary butyl diperadipate, andditertiary butyl dipersuccinate, the said mixture of ingredientshaving-- an improved adhesion to various solid surfaces over the samecomposition which the organic peroxiiie' compound is omitted.

One of the objects of this invention is to improve' the adhesionof'certain silicone rubbers to various surfaces soas togi've a bond atleast as strong: as the cohesive forces of the silicone-- rub beritself.

Another object of this invention is" to improve the adhesion ofsiliconerubbers to variousmetals and siliceous surfaces, such as glassand ce-- ram'ics:

A-stilr further object of this invention is topermit organopolysiloxanescontaining titaniumdioXide-as a; filler, the said organcpolysiloxanesbeing convertible to the" solid elastiestate'; to be bonded easily andquickly to" metal; glass, c'e"- ramic} synthetic plastic surfaces, etc:,soas to;

obtain a bonding zone-without the necessity of using special treatmentsor primers; which-is highlyresistant to"deterioration at elevated t'emp'e'ratures and capable of remaining flexible at verylow temperatures;

Other objects of this inventionwill, become more apparent as thedescription thereof" pro ceeds.

Because of the relativelyinert properties of silicone rubbers,it-hasbeen diificul't toadhere the latter materials to mam solidsurfaces. Heret-o fore the only way knownhas been to primethei surfaceto.- which it'- is: desired to adhere the sill cone rubberwithapr-iming'" agentrand thereaiter applythe silicone rubber inthe?uncured state tethe;saidprimed-surrace: "Imus, inzcope'ndingsmith-Johannsen application Serial No: 77504. 5} filed February 1 1;1949.- (now United: States-Bat ent $601333? issued; J1me 2.4,. 1952:);and; assigned tothe sameassienee as: the: present invention, there aredisclosed ancl claimed methodsfon proving,- the adhesion: or variousorganopoiysiioxanes to diiierent types of surfaces by first priming:thcsurface withaaidisilane corresponding; to'the general; formula:-(R'nSiciX) sL-n where R is a. monovalant hydrocarbon: radical,- X is ahalogenandm'is'aninteger'equai to from 1' to 4; prior to applying: the;organopcl-ysiloctaneto the surface: Inanother:applicationofione of usnamely,RohertSmith-Johennsen-, Serial No; 1 90241;

' filed- October- 14; 1950;.and1assigned'to' the same assignee' as; the:instantv invention; there isdist closed and claimed a method foradhering organopolysiloxanes convertible to the solid elastic stateby:first priming: the: surface" to which the" organopolysiloxane'isto'beladheredzwith a com-- positioncomprising:anhydrolyzableforganosilicate. compound corresponding; togeneral iornufla':

coesii-a" where 1R;- anct R; areeac'h-certain organic groups orhalogenated organic groups. Thereafter, the" heat convertibleorganopolysiloxane; in. this caseone containing: lessr'than 0211x101;percent copoly merized: mono-organosiloxane, is; then capable )ofbein.adhermi;- to thetreatedsurfaceby merely applying; theorgano'poiysiloxane thereto: and:

effecting curing; of the -organopolysilomne by the application of heat.

Although prior techniques for adhering siiinecessary to rcle'an thesuriace tc'i which the siltcone rubber is-=tobe 1 adhered; to: inhibitcorrosion of: the surface in" thezcase of; some: of the metals; to,prime it thereafter with". the proper priming;

agent, andgenerally washingaandsdryingithesur face toremove-anytraceszofi materials which may be deleterious tothebondlhetweenrthe" surfaceand the-silicone rubben. Iii-1addition,veven with" these; many" steps: the; techniques.- required vary"in'manycaseszi-rom- -siirface tolsurface; and vary even among primingagent.

We; have now discovered a? means of incorpor'ting all vthe:desirx'edadhesive: properties in the uncured; organopolysiloxanef convertible tothe solid elastic state; thus making: unnecessary all the special;surface? treatments: and: 'p u preparation of the surface prior toadhering the organopolysiloxane. More particularly, we have discoverdthat the incorporation of a small amount of a particular organicperoxide compound selected from the class consisting of ditertiary butyldiperphthalate, tertiarybutyl hydroperoxide, diperscucoinic acid,ditertiary butyl diperadipate, and ditertiary butyl dipersuccinate, inthe organopolysiloxane together with the cure accelerator which isdifferent from the organic peroxide compound and which may be, forinstance, benzoyl peroxide, tertiary butyl perbenzoate, etc., permitsadhesionof the organopolysiloxane to various surfaces without thenecessary preliminary preparing and priming of the surface with primingagents, This effect was specific to the five organic peroxide compounds,and attempts to use similar organic peroxide compounds wereunsuccessful. We have found that the amount of the adhesive-inducingorganic peroxide compounds .mentioned above is critical and if too largean amount is employed, instead of having adhesion, the silicone rubberacts as though some release or lubricating agent had been incorporatedtherein, due to what is believed an inhibition of the cure. Moreover, wehave also found that theincorporation of one or more of the five organicperoxides mentioned above is only efiective in improving the adhesion oforganopolysiloxanes which contain titanium dioxide as a filler.Organopolysiloxanes using fillers other than titanium .dixoide incombination with the cure accelerator and the organic peroxidecompoundsmentioned above show no improved adhesion and actually exhibitmold release properties, and thuspoorer adhesion over the samecompositioninwhichthe organic per-v oxide compound is omitted.

That the incorporationv of one or more of these five organic peroxidesin small amounts could affect the adhesion properties was entirelyunexpected and in no Way could have been predicted. In this connection,we are not unmindful of Jones.Patent 2,448,530, issued September 7,1948, which discloses some of the organic peroxide compounds mentionedabove but lists these compounds as alternative cure accelerators inplace of benzoyl peroxide. There is no disclosure or teaching in thispatent that the combination of a cure accelerator and these organicperoxide compounds can improve the adhesion of the organopolysiloxanes.As a matter-offact it has been found that some of the organic peroxides,particularly those with which our invention is concerned and which arespecifically mentioned in the Jones patent, when employed alone as cureaccelerators for the organopolysiloxane develop a much poorer degree ofvulcanization or cure over that attained using, e. g., benzoyl peroxide.Moreover, the Jones patent teaches that these particular organicperoxide compounds are used in amounts equivalent to that in which thealternative .cure accelerator, benzoyl peroxide is employed, whichaccording to the examples inthe patent comprise about/2 to,3% of theheatconvertible organopolysiloxane. To use such amounts incur inventionwould, as pointed out above, lead to no improvement in adhesiveproperties and Would give an inferior product having poor physicalproperties,

In order to avoid any question as to the structure .of the organicperoxide compounds with which the present invention is concerned, thefollowingisalistof the formulas for these organic peroxides which havebeen found excluper cent.

sively able to impart improved adhesion of the silicone rubbers tovarious surfaces:

Ditertiary butyl diperphthalate Tertiary butyl hydroperoxide C(CHz)s-OOHDipersuccinic acid CHz-3OOH omcoon g Ditertiary butyl diperadipateHzCfi-OOC(CH5)3 The foregoing organic peroxides are necessarily employedin a relatively small amount as compared to the amount of the cureaccelerator or vulcaniz ing agent used to effect conversionof theorganopolysiloxane to the heatconverted, solid elastic state. Based onthe weight of the organopolysiloxane, We may employ up to 0.5 percent,by weight of the organic peroxide, preferably from about 0.001 to 0.05Amounts in excess of 0.5 per cent when used with the cure acceleratorhave a deleterious effect on the product and on the adhesion of theorganopolysiloxane. The claimed compositions of matter employ thecombination of a cure accelerator other than the organic peroxidecompound and the organic peroxide compound itself. The cure acceleratorsknown heretofore when employed alone, for example, benzoyl peroxide ortertiary butyl perbenzoate, do not have any effect on the adhesion ofthe organopolysiloxane. Also, we havefound that little, if any,vulcanizing influence is imparted by using any of the five organicperoxides alone as vulcanizing agents or cure accelerators for theorganopolysiloxane. Finally, the combination of the cure accelerator andthe organic peroxide compound (or compounds) has the added advantage ofunexpectedly increasing the rate of cure or vulcanization of certainorganic polysiloxanes, particularly those containingincreased amounts ofcopolymerized mono-organopolysiloxanes, e. g., from 0.3 to 0.4. mol percent copolymerized monomethylsiloxanef ,In the specification and in theclaims, for brevity, the convertible organopolysiloxane, which may be. ahighly viscous mass or a gummy, elastic solid, depending on the state ofcondensation, will hereinafter be referred to as convertible.organopolysiloxane or more specifically as convertiblemethylpolysiloxane.

Although convertible .organopolysiicxanes with which the presentinvention isv concerned are well known, for purposes of showing;.persons skilled in the artthe various convertible .organopolysiloxaneswhich may be employed in the practice of the present invention,attention is directed to the convertible organopolysiloxanes disclosed.and claimed in Agens- Patent 2,443,756; issued September 7, 194 8, inSprung et al. Patent 2,448,556, issuedseptember 7, 19458, in SprungPatent 2,484,595, issued October '11, 1949,.in-Krieb-le et a1. Patent2,457,688, issued December 28, 1.948, Hyde Patent 2,490,357, issuedDecember :6, 1949, and in Marsden Patent 2,521,528,. issued September 5,1950. t v

It will. of course be understood by those skilled in the art that otherconvertible organopolysiloxanes containing the same or diflerentsilicon-bonded organic substituents .(e. g., methyl, ethyl, :propyl,phenyl, to'lyl, x-ylyl, benzyl, phenylet'hyl, naphthyl, chlorophenylboth methyland phenyl, etc., radicals), connected to the silicon atomsby carbon-silicon linkages, may. be employed without departing from thescope of. the invention. The particular convertible organopolysiloxaneused is not critical and may be any of those described in the foregoingpatents. which are generally obtained by condensation of a liquidorganopolysi loxane containing an average from about 1.95, preferablyfrom about 1.98, to about 2.2 organic groups per silicon atom. The usualcondensing-agents are those Well 'known in theart and mayinclude forinstance ferric chloride hexahydrate, phenyl phosphoryl chloride,alkaline condensing agents, suchas, potassium hydroxide, sodiumhydroxide,

etc.

These convertible organopolysiloxanes generally comprise polymericdiorganosiloxanes containing at most moi per cent, preferably at most 2mol per cent copolymerized mono-organosiloxane, for example,copolymerized monomethylsiloxane. Generally we preferto. use as thestarting liquid organopolysiloxanefrom which the convertible (forexample heat-convertible) org-anopolysiloxane is: prepared, one whichcontains about 1.995- to 2-50, inclusive, organic groups, for example,methylgroups, per silicon atom and wheremore than about 95%, preferably,99% of the-silicon atoms in the po1ysiloxane contain two silicon-bondedorganic groups, for instance, alkyltgroups, for. example; methyl groups,etc.

The effective .cureaccelerators which. mayv be employed together withthe five organic peroxide compounds mentioned above may be oneof, the.several now well knownin .the art. .for. instance, benzoyl peroxide and.tertiary butylperbenzoate. These; cure a celerators. may. be present. inam nts ran n romabout .5. t as h gh s4 110.8 per .cent preferably,fromabout. 1 to 4 per: cent, by weight, based on the. weight of, theorganopolysiloxane.

The amount of titanium dioxide used may. also vary. depending on theparticularcure accelerae tor and organic. peroxide; compoundemployed, te applica n for ich theh ahcon d, solid, elastic product is intended,the-particua s nq olysil x u d, ta, Gene lly. h

titanium dioxide. may. be. present. in amounts;

varying. for, example, by. weight. from about. .75. to about. 225. partsof. the... titanium dicmide.v per 1-0.0..parts iof the convertibleorganonolysiloxane. It will of course be apparent to those slfilied inthe-art that larger or smaller ratios-citric titani- & um dioxide: mayalso be employed that the amount of titanium dioxide. used is notcriti@- cal in the practice of our-invention.

Generally, the. method whereby the claimed compositions .ofmatter may beprepared. are well known the art. For the most part the convertibleorganopolysiloxane, filler, cure .ac celerator, and one or more of theorganic per oxide compounds mentioned above are advantageously mixedtogether on rubber compound.- ing rolls until a homogeneous mixture or:sheet is obtained, depending. -.onrwhetherthe conver' tibleorganopolysiloxane used is in the form of a viscous mass or solidelastic product. The mix- 1 ture. is advantageously allowed to age, e.'g., by

standing at room temperature, for about 24 to 48 hours prior tousing'it. Thereafter, themixture is applied in any desired thickness tothe solid surface to which" adhesion is desired. It will be found thatmere application of the organopolysiloxane to the respective surface.will result in marked pressure-sensitive adhesion between the surfaceand the convertible organm polysi-loxane. Thereaft.er,. the totalassembly may be subjected to a heat-curing operation, preferably underpressure, for example, at term peratures ranging from about to 200 C.for varying lengths of time depending upon thetemperatures used, forinstance, from about. a few seconds to 25 or several hours. This willgenerally convertthe organopolysiloxane to a solid elastic product whichmay then-be further-heattreated at higher temperaturesof" the order offromabout' 200 to 250 C". for longer periods of time, for example, forabout 1 to '24 hours: in

order to obtain the ultimate physical properties in the heat-cured,solid, elastic product.

In addition to effecting adhesion of the finally cured, solid, elasticorganopolysiloxane or silicone rubber to many surfaces as, for example,porcelain enamel, glass, aluminum, steel, copper, various plastics, suchas, for example, polymeric monochlorotr-ifluoroethylene polymers, wehave also found that certain additional improvements in the propertiesofthe'organopolysiloxane itself are also obtained; Thus, it has beenfound; that improvements in softness and strength over regularly curedorganopolysiloxanes in which the organic peroxide compounds are omitted.result from using these organic. peroxides.

In order. that those skilled in theart may b.et-. ter understand how thepresent. invention may be practiced, the following examples are givenbyway of'illustr-ationand not by way of limitation; Allare by weight.

Example I In this example, a heat convertible compound was prepared bymixingtogether 66 parts titanium dioxide, 33 parts of a heat-curablesolid, elastic methylpolysilox-ane containingan average of about 1,952.6methyl groups per siliconatoni andobtained by condensing with-ferricchloride hexahydrate a liquid methyl polysiloxane containingapproximateiy 1 .996 methyl groups silicon atom, dddnart benzoylperoxide, anailili part1 clitertiary. butyl .diperphthalate.'l-higsiltconegnm adhesive; wasapplied to the surface or a .degreased.copper. surface and pressed underiight pressure (about. iilto. 25; p. e.i.) for id minutes atabout; 1.50? C. Thereafter, the totai assemblyWasremoved. from the press .and sub jected tofurther. heat: treatment.at about 2133 C: .for. Zhhoura Attthe :end of-s this time'it was foundthat the bond 'betwecn-ithe silioonerubber and the'copper surface was asstrong as the cured silicone rubber itself and attempts to remove thesilicone rubber from the copper surface resulted only in tearing of thesilicone rubber itself. When the same heat-convertible silicone rubberadhesive minu the ditertiary butyl diperphthalate was applied to thecopper and treated in the same fashion as above, after the final heattreatment it was found that there was no adhesion between the curedsilicone rubber and the copper, and the silicone rubber could be peeledeasily from the surface thereof.

Example II In this example, each of the five organic peroxide compoundsmentioned above was incorporated in a silicone adhesive paste comprising50 parts titanium dioxide, 50 parts of hydrolyzed dimethyldichlorosilanecontaining about 0.35 to 0.4 mol per cent methyltrichlorosilane (thehydrolysis product being condensed with 0.2 per cent, by weight, ferricchloride, based on the weight of the oily hydrolysis product, until ahighly viscous methylpolysiloxane was obtained), and 1.5 parts benzoylperoxide. This adhesive paste was applied to surfaces such as steel,copper, glass, aluminum, and porcelain enamel in about a -mil thickness,and aluminum foil was applied over the adhesive. Thereafter each of theassemblies was heat treated in the same manner as described above inExample I. The amounts of organic peroxide in the formulations werevaried for all the surfaces and the following table shows the optimumpercentages of each of the organic peroxide compounds used in thevarious examples.

In each case regardless of the under surface, after heat treatment ofthe total assembly, 1. e., of the solid surface and the filledheat-convertible methyl polysiloxane, there was obtained a satisfactorybond between the surface and the solid elastic organopolysiloxane. Thealuminum foil was also well adhered and formed an integral part of eachassembly. The ditertiary butyl diperphthalate appeared to give the bestand most consistent results with all the surfaces tried.

Example III Cured silicone rubber was adhered to a ferrous surface bymeans of the silicone adhesive paste described in Example II usingditertiary butyl diperphthal ate only if a small amount of aluminumpowder in an amount equal to from about 2 to 10 per cent, by weight,based on the weight of the total adhesive paste was incorporated.Thereafter it was found desirable to use a higher curing temperature,for example, about 200 C. initially in order to effect a satisfactorybond between the metal and the cured silicone rubber. Aluminum powderwas not required to effect a satisfactory bond when tertiary butylhydroperoxide was employed in place of the ditertiary butyldiperphthalate.

' We may employ other convertible organopolysiloxanes of the varioustypes described previously in the different patents mentionedheretofore. In addition the particular-heat convertibleorganopolysiloxane, besides having been condensed by means of ferricchloride hexahydrate, may also have been condensed by other condensingagents many examples of which also have been given above. Moreover othercure accelerators in addition to the one employed in the foregoingexamples may also be employed, and in other concentrations thereof, forinstance, in amounts ranging from 0.5 to 4 to 6 per cent, by weight,based on the weight of the convertible organopolysiloxane may be used.

Our invention is applicable for adhering the convertibleorganopolysiloxanes to other glass surfaces, for example, glass tape,glass fibers, glass fiber sheets, etc. In the latter instance, glasscloth made from glass fibers may be coated with the compositions ofmatter herein described and thereafter heated to effect curing .of thesilicone rubbers to various metal surfaces as well as to varioussiliceous, for example, glass or ceramic surfaces. Electrical conductorssuch as copper conductors, can be coated with these claimed compositionsof matter merely by extrusion of the filled and modifiedheat-convertible organopolysiloxane and thereafter passed through anoven and cured at elevated temperatures to give a tightly adherentinsulating coating. In addition, it is possible to make seals withvarious types of equipment including vacuum seals for pumpless powerrectifiers, seals in steam irons, etc. Our invention is adaptable forsealing the casings containing anodes and cathodes found in electricaldischarge devices.

Our invention obviates the necessity of using large amounts of benzoylperoxide to obtain a satisfactory bond and also permits the use ofeasily prepared convertible polysiloxanes. Heat resistant properties arematerially affected adversely when too large amounts of the cureaccelerator, e. g., benzoyl peroxide, are employed.

What we claim as new and desire to secure by Letters Patent of theUnited States is:

1. A composition of matter comprising (1) a titanium dioxide-filledorganopolysiloxane convertible to the cured, solid, elastic state inwhich the organic groups are selected from the class consisting ofalkyl, aryl, aralkyl, and alkaryl radicals, the said organic groupsbeing present in the ratio of from about 1.98 to 2.2 organic groups persilicon atom, (2) a curing agent for (1) selected from the classconsisting of benzoyl peroxide and tertiary butyl perbenzoate, and (3)an organic peroxide compound present in an amount up to 0.5%, by weight,based on the weight of the organopolysiloxane, the said organic peroxidecompound being selected from the class consisting of ditertiary butyldiperphthalate, tertiary butyl hydroperoxide, dipersuccinic acid,ditertiary butyl diperadipate, and ditertiary butyl dipersuccinate.

2. A composition of matter comprising 1) a,

assua e titanium dioxidee-filsled methylpolysiloxane contwining anaverage "of from about 138 t'o 2:2 methyl groups per silicon atom andbeing convertible to the solide'lastic state, (2 a curing agent for 01*)selected rom the class consis'tin'g of benzoyl peroxideand tertiary'bu'tyl perbenzo- :ateyand (3) an organic peroxide compound present anamoun'tnp to :5=%, by weight, basedon theweight of theorgan'opolys'iloxane, the said organic peroxide compound being selectedfrom the class consis'tingOf ditertiary butyl "diper- \pht'halate,"tertiary butyl hydroperox'ide, dipersuccinic acid, ditertiary butyldiperad-ipate, di-tertiary bu-tyl olipersuccir-iate.

3. A composition of matter comprising (1) a titanium dioxide-filledorganopolysiloxane in which the organic groups are selected from'theclass consisting .of sallkyl, aryl, zara lkyl, and alkaryl radicals andare present in the ratio of from (about 1:98 -to 2.2 organic groups persilicon atom, the said .organopolysiloxane being convertible to thesolid elastic state, (2) benzoyl peroxide, and (3) an organic peroxidecompound present in an amount up to 0.5%, by weight, based on the weightof the aforesaid organopolysiloxane, the said organic peroxide compoundbeing selected from the class consisting of ditertiary butyldiperphthalate, tertiary butyl hydroperoxide, dipersuccinic acid,ditertiary butyl diperadipate, and ditertiary butyl dipersuccinate.

4. The process for adhering silicone rubber to various surfaces whichcomprises (1) forming a mixture of ingredients comprising (a) titaniumdioxide-filled organopolysiloxane in which the organic groups areselected from the class consisting of alkyl, aryl, aralkyl, and alkarylradicals and in which there are present an average of from about 1.98 to2.2 organic groups per silicon atom, the said organopolysiloxane beingconvertible to the solid elastic state, (b) a curing agent for (a)selected from the class consisting of benzoyl peroxide and tertiarybutyl perbenzoate, and (c) an organic peroxide compound present in anamount up to 0.5%, by weight, based on the weight of theorganopolysiloxane, the said organic peroxide compound being selectedfrom the class consisting of ditertiary butyl diperphthalate, tertiarybutyl hydroperoxide, dipersuccinic acid, ditertiary butyl diperadipate,and ditertiary butyl dipersuccinate, and (2) applying the said mixtureof ingredients to the surface to which it is desired to adhere the saidfilled organopolysiloxane.

5. The method of adhering a silicone rubber to various surfaces whichcomprises (1) forming a mixture of ingredients comprising (a) a titaniumdioxide-filled methylpolysiloxane containing an average from about 1.98to 2.0 methyl groups per silicon atom and being convertible to the solidelastic state, (b) benzoyl peroxide, and (c) an organic peroxidecompound present in an amount up to 0.5%, by weight, based on the weightof the methylpolysiloxane, the said organic peroxide compound beingselected from the class consisting of ditertiary butyl diperphthalate,tertiary butyl hydroperoxide, dipersuccinic acid, ditertiary butyldiperadipate, and ditertiary butyl dipersuccinate, (2) applying theaforesaid mixture of ingredients to the surface to which adhesion isdesired, and (3) heating the total assembly until a firmly bondedproduct is obtained.

6. A composition of matter comprising (1) a titanium dioxide-filledmethylpolysiloxane containing an average of from about 1.98 to 2.2methyl groups per silicon atom and being con- 1.0 wertible to the solidelastic state, 2) benzoyl peroxide, and (3') ditertiary butyldiperphthalate, the latter being present in an amount up to 0.5%,by-weig'h't,based on'theweightof the methy-lpolysilexane.

7. composition-of matter comprising (1) a titanium dioxide-filledmethylpdlysiloxane containing an average of from about 1:98 to 2.2methyl groups per silicon atom and being 'con- "vertib'le to the solidelastic "state, (2) benzoyl peroxide, and (3) tertiary butylhydroperoxide, the latter being present in an amount up to 0.5% "byweight, based on the weight of the methylpolys'iloxane.

'8. A composition of matter comprising (1) a titanium -dioxide-fille'dmethylpolysiloxane conaverage of from about "1.98 to 2.2 methyl g-roupsper silicon "atom and being convertible-to the solid elastic state, =(2)benzoyl peroxide, and (3) dipersuccinic acid, the latter being presentin an amount up "to 0.5% bywei'ght, based on the weight oi? themethyl-polysiloxane.

9. A composition of matter comprising (1) a titanium dioxide-filledmethylpolysiloxane containing an average of from about 1.98 to 2.2methyl groups per silicon atom and being convertible to the solidelastic state, (2) benzoyl peroxide, and (3) ditertiary butyldiperadipate, the latter being present in an amount up to 0.5%, byweight, based on the weight of the methylpolysiloxane.

10. A composition of matter comprising (1) a titanium dioxide-filledmethylpolysiloxane containing an average of from about 1.98 to 2.2methyl groups per silicon atom and being convertible to the solidelastic state, (2) benzoyl peroxide, and (3) ditertiary butyldipersuccinate, the latter being present in an amount up to 0.5% byweight, based on the weight of the methylpolysiloxane.

11. The method of adhering a silicone rubber to various surfaces whichcomprises (1) forming a mixture of ingredients comprising (a) a titaniumdioxide-filled methylpolysiloxane containing an average of from about1.98 to 2.2 methyl groups per silicon atom and being convertible to thesolid elastic state, (b) benzoyl peroxide, and (a) tertiary butylhydroperoxide, the latter being present in an amount up to 0.5%, byweight, based on the Weight of the methylpolysiloxane, (2) applying theaforesaid mixture of ingredients to the surface to which adhesion isdesired, and (3) heating the total assembly until a firmly bondedproduct is obtained.

12. The method of adhering a silicone rubber to various surfaces whichcomprises (1) forming a mixture of ingredients comprising (a) a titaniumdioxide-filled methylpolysiloxane containing an average of from about1.98 to 2.2 methyl groups per silicon atom, and being convertible to thesolid elastic state, (b) benzoyl peroxide, and (c) dipersuccinic acid,the latter being present in an amount up to 0.5%, by weight, based onthe weight of the methylpolysiloxane, (2) applying the aforesaid mixtureof ingredients to the surface to which adhesion is desired, and (3)heating the total assembly until a firmly bonded product is obtained.

13. The method of adhering a silicone rubber to various surfaces whichcomprises (1) forming a mixture of ingredients comprising (a) a titaniumdioxide-filled methylpolysiloxane containing an average of from about1.98 to 2.2 methyl groups per silicon atom, and being convertible to thesolid elastic state, (b) benzoyl peroxide, and (c) 1 l ditertiary butyldiperphthalate, th latter being present in an amount up to 0.5%, byweight, based on the weight of the methylpolysiloxane, (2) applying theaforesaid mixture of ingredients to the surface to which adhesion isdesired, and

(3) heating the total assembly until a firmly bonded product isobtained.

14. The method of adhering a silicone rubber to various surfaces whichcomprises (1) forming a mixture of ingredients comprising (a) a titaniumdioxide-filled methylpolysiloxane containing an average of from about1.98 to 2.2 methyl groups per silicon atom, and being convertible to thesolid elastic state, (b) benzoyl peroxide, and (c) ditertiary butyldiperadipate, the latter being present in an amount up to 0.5%, byweight, based on the weight of the methylpolysiloxane, (2) applying theaforesaid mixture of ingredients to the surface to which adhesion isdesired, and (3) heating the total assembly until a firmly bondedproduct is obtained.

15. The method of adhering a silicone rubber to various surfaces whichcomprises (1) forming a mixture of ingredients comprising (a) a titaniumdioxide-filled methylpolysiloxane containing an average of from about1.98 to 2.2 methyl groups per silicon atom, and being convertible to thesolid elastic state, (b) benzoyl peroxide, and (c) ditertiary butyldipersuccinate, the latter being present in an amount up to 0.5 byweight, based on the weight of the methylpolysiloxane, (2) applying theaforesaid mixture of ingredients to the surface to which adhesion isdesired, and (3) heating the total assembly until a firmly bondedproduct is obtained.

ROBERT SMITH-JOI-IANNSEN.

CURTIS S. OLIVER.

References Cited in the file of this patent UNITED STATES PATENTS

1. A COMPOSITION OF MATTER COMPRISING (1) A TITANIUM DIOXIDE-FILLEDORGANOPOLYSILOXANE CONVERTIBLE TO THE CURED, SOLID, ELASTIC STATE INWHICH THE ORGANIC GROUPS ARE SELECTED FROM THE CLASS CONSISTING OFALKYL, ARYL, ARALKYL, AND ALKARYL RADICALS, THE SAID ORGANIC GROUPSBEING PRESENT IN THE RATIO OF FROM ABOUT 1.98 TO 2.2 ORGANIC GROUPS PERSILICON ATOM, (2) A CURING AGENT FOR (1) SELECTED FROM THE CLASSCONSISTING OF BENZOYL PEROXIDE AND TERTIARY BUTYL PERBENZOATE, AND (3)AN ORGANIC PEROXIDE COMPOUND PRESENT IN AN AMOUNT UP TO 0.5%, BY WEIGHT,BASED ON THE WEIGHT OF THE ORGANOPOLYSILOXANE, THE SAID ORGANIC PEROXIDECOMPOUND BEING SELECTED FROM THE CLASS CONSISTING OF DITERTIARY BUTYLDIPERPHTHALATE, TERTIARY BUTYL HYDROPEROXIDE, DIPERSUCCINIC ACID,DITERTIARY BUTYL DIPERADIPATE, AND TITERTIARY BUTYL DIPERSUCCINATE.